Which of the following aggregation commands in MongoDB does not support sharded collections?

Question

Options

• AmapReduce
• Bgroup
• Caggregate
• DAll of the above

• A
  3% (1)
• B
  91% (31)
• C
  6% (2)

Explanation

group is the command that does not support sharded collections - attempting to run it on a sharded collection throws an error. This is a known limitation of the legacy group command, which predates MongoDB's more mature distributed execution capabilities.

Why the distractors are wrong:

• A (mapReduce): mapReduce does support sharded collections - MongoDB can run the map phase across shards and merge results.
• C (aggregate): The aggregation pipeline fully supports sharded collections, distributing pipeline stages across shards efficiently.
• D (All of the above): Incorrect because only group is unsupported on sharded collections.

Memory tip: Think "group can't handle the crowd" - just as a group command might struggle in a large crowd, MongoDB's group command can't handle data spread across multiple shards. If you need grouping on sharded data, use the aggregation pipeline's $group stage instead.

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